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Too much of a bad thing can be good in brain tumors

By Bill Hathaway

March 25, 2015

DNA mutations can cause cancer but in some cases, more mutations may mean a better prognosis for patients. A Yale-led comprehensive genomic analysis of more than 700 brain tumors has revealed one such subtype of the most malignant brain tumor, called glioblastoma, or GBM. This subtype possesses thousands of tumor-specific DNA errors or mutations instead of dozens observed in most glioblastoma cases. It is also associated with longer survival.

The findings, reported in Journal Neuro-Oncology, suggest it may be possible to develop personalized treatments for more aggressive forms of brain cancer, including immunotherapy for these hyper- or ultra-mutated tumors, said Murat Günel, professor and chair of neurosurgery, who leads the Brain Tumor Research Program at Yale and Smilow Cancer Hospital at Yale-New Haven Hospital.

“We have been able to translate various complementary cutting-edge genomic technologies, which were once solely research tools, to our clinical programs to analyze individual cancers,” said Günel, who is also a professor of genetics and a researcher for the Yale Cancer Center. “We can now gain comprehensive understanding of the molecular make-up of a cancer to pinpoint specific vulnerabilities and leverage these weak spots for precision treatments in our Recurrent Brain Tumor Treatment Program.”

While as many as 10,000 mutations were found in the newly described subset of glioblastomas, a more typical tumor contains less than 100. This counterintuitive pattern has also been observed in gynecological and colon cancers: An extraordinary number of mutations means a better chance of survival.

One theory holds that cells with greater number of mutations are able to trigger an aggressive immune system response against cancer cells, while cells with fewer mutations might escape detection, Gunel said.

Although the number of GBMs in this newly identified group is small, the use of standard chemotherapy in some cases has been shown to inadvertently result in a hyper-mutated tumor. Indeed, the drug temozolomide, used as the first line of chemotherapy in GBM, has been shown to sometimes increase mutations.

“But perhaps the naïve immune system is not strong enough to eliminate the cancer cells in these brain tumors,” Gunel noted.

However, if a new generation of immunotherapy drugs called checkpoint inhibitors were used in these hyper-mutated tumors, perhaps more cancer cells might be targeted for destruction, he said. Clinical trials currently underway might be improved by considering the molecular genetic make-up of the individual tumor, he concluded.